As an attempt to achieve maximum production of beneficial proteins (such as EPO with high economic value-added) in the medicinal field, mass production methods using cell culture techniques have been mainly used.
Korean Patent Application No. 94-12082 discloses an expression vector containing a modified recombinant human erythropoietin (rhEPO) gene. Despite feasibility of mass production of EPO in the animal cell line COS-7 (ATCC CRL 1651, African Green Monkey Kidney Cell) transformed with the same expression vector, this technique disadvantageously suffers from a cumbersome need of continuous transformation, which makes it unsuitable for industrial-scale production of a target protein. Further, Korean Patent No. 10-0232640 and Korean Patent Application Publication No. 1999-0075254 also disclose the production of EPO by transgenic cell line culture. However, these cell culture methods still suffer from disadvantages such as high production costs due to use of animal blood as a culture medium, and requirement of expert and sophisticated knowledge in the culture technique.
On the other hand, the production of beneficial proteins using transgenic animals is attracting a great deal of interest due to having advantages such as easy and convenient production, isolation and purification of target proteins and maintenance of superior activity, as compared to conventional cell culture techniques, because the target proteins are contained in body fluids secreted by animals. For example, Korean Patent Application Publication No. 2004-0081456 discloses a transgenic animal for the production of EPO in porcine milk, using a whey acidic milk protein promoter (WAP).
As a result of a variety of extensive and intensive studies and experiments to solve the problems as described above and to develop a mammary gland-specific promoter with high-efficiency expression of a target protein in milk, the inventors of the present invention succeeded in sequencing of a beta-casein gene and a promoter thereof. The present invention has been completed based on this finding.